It is known to make sealing and potting compounds, i.e. compositions, from polymers and additives. Sealing compounds made from thermoplastic polymers, such as polyisobutylene, butyl rubber or thermoplastic rubbers can be handled relatively easily at elevated temperatures in suitable machines. Any residues may remain in the equipment and can be rendered flowable by the supply of heat so that they can be reused.
Single-component reactive sealing compounds which will vulcanize or thermally set when exposed to air moisture or oxygen, such as silicone-based sealing compounds, can also be handled without major difficulty. Such sealing compounds are used, e.g. to seal composite insulating glass panes. Cold-setting binary synthetic rubbers, e.g., such rubbers based on liquid polysulfide polymers or on polyurethanes, are used for the same purpose.
Binary compounds of high viscosity intended for use as sealing compounds, coating compounds or potting compounds are processed in suitable machines under high pressure.
In such equipment, the two components of the compound are fed from two separate supply vessels or containers and are proportioned to provide the proper mixing ratio. Thereafter the two components are brought together in a mixing head and a homogeneous mixture is made in a static and/or dynamic mixer.
To ensure that the machine will not be clogged by cured or set material, those parts of the machine which are filled with the mixture of components must be flushed when the operation is interrupted for a long time or is terminated. Such parts include the mixing head, the mixer, flexible tubing, any spray gun or nozzle.
Such flushing is effected in known manner by means of solvents or solvent mixtures which can dissolve the pastelike unreacted material. Such solvents may consist, e.g. of chlorinated hydrocarbons, such as methylene chloride.
It is also known to use rinsing systems in which no solvent is employed but a rinsing is effected with one component of the binary compound. In this case one attempts to inhibit the curing reaction by a strong dilution of one of the components of the mixture (EP-A 0059 380, U.S. Pat. No. 3,989,228).
But considerable difficulties are involved in that practice, particularly with highly reactive compounds since cured material can build up progressively on the surfaces or pipes and containers if the reactive mixture remains in the plant or equipment for an excessively long time owing to an insufficient rinsing section of the solvent, which is circulated by a pump.
This will finally result in a clogging and shutdown of the plant or system.
Another difficulty involved in a rinsing with solvents resides in that the reactive material will continue to react in the solvent if a concentration limit of about 10% is exceeded. That continued reaction results in the formation of gel-like precipitates so that the solvent can no longer be pumped and must be discarded.